Motor control



April 26, 1949. z. w. WHITEHOUSE MOTOR CONTROL Filed Oct. 50, '1945 INVENTOR. ZfBULO/V W WH/TE/7OUSE ATTORNEYS Patented Apr. 26, 1949 cassava moron oouraor.

Zebulon W. Whltehouse, ilanton, Ohio, asslgnor to Republic Steel Corporation, Cleveland, Ohio, a corporation of New .iersey Application October 3d, 1945, Serial No. 625,478

it @laims till. 318-434) ii ii /i invention relates to control systems and o seems particularly control systems for motors be operated under such conditions as subjected to the possibility of jamming or c object of my invention is to protect electric rs whether oi the series, shunt, or compound e from burning out or from over-heating in event heing stalled or jammed or sch ted to excessive torque load, especially after "rig resistors have been cut out. r ohject of my invention is to limit the icing cu hi; or stalling current in a motor -ned peak value independent of ores of accelerating peaks which may he cmin accelerating the motor or bringing it reed when it is initially being started, or

the line.

eject of the invention is to provide ut protection which is quick-operating. seer object is to provide for motor proin which accelerating peaks may be per- "-1- to continue for predetermined lengths of when the motor is being placed on the line, art am current protection is provided substanliy instantaneously in case jamming current stallin current rises to a predetermined value after the motor has been started, in the event the motor should be subjected to excessive torque load or should be stalled.

Still another object of my invention is to provide jam current protection at current values independent of accelerating current peaks emoyed in placing the motor on the line, and to providejam current protection at a. current value substantially smaller than the accelerating peaks permitted when the motor is first started or placed on the line. v

Another object is to provide jam current protection responsive to a given current value while acceleration resistance is connected in series with the motor and exceedingly rapid acting jam current protection responsive to a. different current value after all of the acceleration resistance has been excluded.

Other and further objects, features and advantages will become apparent as the description proceeds.

In carrying out my invention in its preferred form, I provide a conventional starting system having a starting resistance with a plurality of sections in series with each other and with the motor armature, or what amounts to the same thing-a plurality of starting resistors in series, with accelerating contactors connected in reor the separate starting resistors.

Alan

spective loop circuits for successively cutting out or shunting the starting resistance sections In addition provide a separate jam current limiting resistor (or resistance section) in series with the starta resistance means and having an independent jam current contactor which is normally closed for cutting out the jam current resistance. The jam contactor has an actuating windin conn the loop circuit or and in series with one o" e accelerating contactors, preferably the last accelerating contactor to close when the motor is started or placed on the line.

better understanding oi the invention will be afforded by the following detailed description considered in conjunction with the accompany drawing, and the scope of the invention will he in the accompanying claims.

" the drawing:

g. i is a circuit diagram of an illustrative embodiment of my invention and Fig. 2 is a circuit diagram of a modification.

Although my invention may be employed to advantage in motor starting systems having any number of steps of increase of current or of cutting out starting resistors, for the sake of simplicity in the drawing and description, I have shown an embodiment of the invention in which only two steps of starting resistors are employed for bringing the motor up to speed and connecting it directly across the line. The invention may be employed in connection with A.-C. or Lil-0., series, shunt, or compound wound motors with or without reversing connections, but for the sake of illustration the invention will be described in connection with a series wound directcurrent motor.

as shown in Fig. 1 of the drawing, there is a motor having an armature ll in series with a series field winding 52. Current supply terminals l3 and id are provided which, in the arrangement illustrated, are represented as being the positive and negative terminals respectively of a direct-current supply source.

A conventional motor starter is provided which is preferably an automatic starter including steps of starting impedance, which may take the form of sections of resistance l5 and IS in series with the motor H-IZ and the current supply terminals l3 and I4.

Preferably, a starting contactor I1 is provided having a pair of normally-open main-line contacts l8 in series with the starting resistor sections l5 and I6, and the motor armature I I in the main line to the supply terminals l3 and H.

A plurality of accelerating contactors are also provided, one for each of the starting resistor sections. In the specific arrangement described with two starter resistor sections, there is an accelerating contactor l9 having a pair of normally open main line contacts 2| adapted to shunt the initial step of starting resistance or the initial starting resistor section l5, and there is a final accelerating contactor 22 having a pair of normally open main line contacts 23 adapted to shunt out the final step of starting resistance or the final resistor section i6. As will be explained more in detail hereinafter, means are provided for causing the starting contactors l9 and 22 to operate successively closing the contacts I8, 2| and 23. The specific means utilized for causing the contacts to operate in succession do not however constitute a part of my present invention.

In order to prevent the motor H from over heating or burning out in the event that excessive torque load should be applied thereto or it should be stalled or jammed after it has been brought up to speed, or after the contacts l8, 2| and 23 have been closed, means are provided for inserting current-limiting resistance in series with the armature ii. Preferably a separate, independent jam resistor 24 is provided which is connected in series with the armature H and the main line. For preventing the jam resistor 24 from being effective except when needed, a jam contactor 25 is provided having a pair of normally closed contacts 26 connected across the jam resistor 24. Means are provided for causing the jam contactor 25 to operate automatically, whenever the current through the armature Ii exceeds a predetermined value after the contactor 22 has closed. Preferably the arrangement is such that the jam resistor 24 may be introduced in the circuit upon the occurrence of a Jam current of a lower peak value than the accelerating peaks permitted upon closure of the accelerating contactors before the last, in this case, lower than the accelerating peaks which occur upon closure of the contactors i1 and |9. To this end the jam contactor 25 has an actuating winding 21 preferably not connected directly in series with the main line to the supply terminals |3 and I4, but in series with one of the accelerating contactors. Preferably, as illustrated, the jam contactor actuating winding 2'! is connected in series with the last accelerating contactor 23 so that the jam resistor 24 and the jam contactor 25 can not come into operation until all of the accelerating contactors have been closed and the motor II has been placed directly across the line.

In the specific arrangement illustrated for causing the accelerating contactors i9 and 22 to operate ln succession in response to reduction of accelerating current to predetermined values, shunt windings actuated by a separate control circuit are provided. The first accelerating contactor i3 is provided with a shunt winding 28 and the accelerating contactor 22 is provided with a shunt winding 29. The main contactor I! is provided with an actuating winding 3| adapted to be energized from the supply terminals l3 and I4 through a starting switch 32. As shown, the main contactor I1 is provided with normally open auxiliary contacts 33 for preventing the energization of the contactor i9 until the contactor IT has been closed; likewise the first accelerating contactor I9 is provided with normally open auxiliary contacts 34 for preventing the second auxiliary contactor 23 from being actuated until after the contactor [9 has operated.

An acceleration relay 3! is provided for preventing the contactor l3 from operating {or a time interval after the contactor I1 closes. and a similar acceleration relay 33 is provided for preventing the contactor 22 from operating {or a time interval after the contactor l3 closes. The relays 35 and 33 are preferably arranged to give time-current acceleration, holding their contacts open for a time interval which is greater with greater values of current. The relays 35 and 35 may be of any suitable type but preferably are similar to the acceleration relay disclosed in Patent No. 1,980,736 issued to Lev A. Trofimov on November 13, 1934. The relay 3! comprises a series winding 31 interposed in the line leading to the terminal l4, and normally closed contacts 38 connected in the control line in series with the actuating winding 23 of the first acceleration contactor I3. The relay 33 has a series winding 38 and normally closed contacts 43. The winding 39 is connected between a Junction terminal 4| of the starting resistor sections l3 and I5 and a junction terminal 42 between the pairs of accelerating contacts 2| and 23; and the contacts 40 are in series with the actuating winding 23 of the accelerating contactor 22.

In the arrangement illustrated in Fig. 1, when the motor is to be started, the switch 32 is closed energizing the winding 3| of the contactor [1 thereby to close both the main contacts I8 and the control contacts 33. Closure of the contacts l3 completes a circuit from the terminal l3, through the armature H, the field winding I2, the normally closed contacts 23, the starting resistor sections I3 and I3, the winding 31, and the contacts l3 to the supply terminal |'4. Closure of the control contacts 33 completes a circuit from the terminal |3 through the conductors 43, 44 and 45, the winding 23 of the first accelerating contactor IS, the normally closed contacts 38, the now closed contacts 33, and the conductor 46 to the supply terminal I 4. Before the contactor is can operate in response to completion of the above described circuit through its operating winding 28, the normally closed contacts 38 of the relay 35 open in response to energization of the winding 31 by the rise of acceleration current flowing to the motor. After a time interval dependent upon the magnitude of the motor current during the time interval and as described in the above mentioned Troflmov patent, the contacts 33 reclose, to complete the circuit for the winding 23 thereby to cause operation of the contactor l3 and closure of the contacts 2| end thereof. Closure of the contacts l3 completes a short circuit around the resistor section l5 causing an increase in the voltage applied to the armature The sudden rise in current through the short-circuiting loop including the contacts |3 and the winding 33 or the relay 33 causes opening of the contacts 43. The contacts 40 remain open for a time interval dependent upon the magnitude of the motor current flowing during the interval and then reclose to complete an operating circuit for the winding 23 01 the lastaccelerating contactor 22. The circuit for the winding 23 is from the terminal l3 through the conductor 43, the winding 23, the now closed contacts 40 and 34, and the conductor 43 to the terminal I4.

Closure of the contacts 22 completes a short circuit around the resistor section I! through the winding 21 of the jam conductor 23. The motor is now connected directly across the terminals l3 and I4 without series resistance eflectively in the circuit. The foregoing sequence of acceleration switch operating takes place whether the motor rotates or not and is timed in proportion to the magnitude of the motor current, a longer time being required to complete the sequence if the motor is heavily loaded than if it is lightly loaded,

Owing to the fact that accelerating current peaks are usually of relatively short duration while the motor is being brought up to speed, and owing to the fact that in order to bring the motor up to speed with the desired rapidity the accelerating or starting current must reach values of several times the normal running current value, the resistance values of the several starting resistance sections are so selected and the timing relays so adjusted that the acceleration current reaches values considerably in excess of the amount which could safely be allowed to pass through the motor during normal running. Accordingly, when the motor is operated under such conditions that, after being energized, it may become jammed or stalled, it is desirable to provide jamming protection responsive at a lower value of motor current than the peak values occurring during acceleration. In the arrangement illustrated in Fig. 1, it will be observed that the jamming contactor 25 cannot be energized and does not have its operating winding 21 connected in the motor circuit until after all of the accelerating contactors have operated. Accordingly, the acceleration current peak that occurs upon initial connection of the motor to the source and the current peaks that occur upon closure of the acceleration contactors preceding the last accelerating contactor may be in excess of the pick-up current value of the contactor 25. Since the operating winding 21 of the jamming contactor is disconnected until the last acceleration contactor closes, the pick-up current value of the jamming contactor 25 may be reduced below the acceleration current peaks thereby rendering the protective means faster operating and preventing false and premature operation of the jamming contactor 25 thereby not to interfere with fast motor starting.

After all the accelerating contacts, including the last accelerating contact 23, have closed and the motor is directly connected to the line, the jamming contactor 25 is in condition to operate and if the motor current should exceed the value at which it will be safe to permit current to flow with the armature I I jammed or stalled, the contacts 26 open so as to introduce the jam resistor 24 and limit the current flow to the safe value. Inasmuch as the jam resistor 24 is introduced into the circuit only after the motor has been connected across the line, its value may be chosen independently of the value of the resistances of the starting resistors l5 and i6; and may be different from the total starting resistance or the resistance of any one of the starting resistors or resistor sections or any combination of such sections. Consequently, the jam or stalling current to which the current flow is limited when the motor is jammed or stalled or encounters excessive torque load, may be selected independently of the values of resistance utilized in the starting i resistor and independently of the values of current controlled by the accelerating contactors and starting relays. In consequence the optimum value of -motor acceleration current may be chosen and the optimum value of maximum permitted stalling or jamming current may be chosen up again. This cycle would be repeated until the jam condition is removed or the overload protective means (not shown) for the motor responds. By use of the separate resistor 24, this pumping action is prevented merely by selecting the proper resistance value.

The jam contactor 25 is preferably designed to be extremely rapid in operation. For example, many of the moving parts may be made of light alloys and the distance of armature travel is preferably made as small as possible. The speed of operation of the contactor 25 under jam conditions may be further increased by having the pick-up current value of the contactor below the peak values of the acceleration current. Heretofore, reduction in the pick-up current value of jam protection means even to values but slightly above the acceleration current peaks has not been successfully obtained except by the use of a series of relay controlling a separate contactor or contactors with he inherent delay present in such an arrangement. By use of a series wound contactor connected as above described, the response to a jam condition is substantially instantaneous. The jam current causing operation of the contactor can be below the acceleration peaks and the use of a separate jam resistor makes it a simple matter to prevent pumping.

For the sake of simplicity only three steps of acceleration (two steps of starting resistance) and a single step of jamming current limitation have been shown in Fig. 1 of the drawing, but it will be understood that the invention is not limited to utilizing only a single section jam current limiting resistor 24 and utilizing only a single jamming current contactor set for a single value of current.

Although my invention is not limited thereto, the arrangement for cutting in the jam current limiting resistor 24 is preferably a series winding carrying the motor current, such as the actuating winding 21 in series withthe last accelerating contacts 23in order to insure positive action and opening of the contacts 26 whenever the jam current exceeds the desired value. In this manner, the operation of the Jam contactor is not dependent upon continuity of a control circuit or upon the absence of sticking of a separate operating relay, for example.

In the modification of Fig. 2 a jam switch 50 which may be either a relay or contactor is added to the system of Fig. 1 and has an operating winding 5! interposed in the line leading to the terminal i4 and normally closed contacts 52 and 52 interposed in the conductors 46 and 49, respectively. The jam switch 50 preferably has a relatively large air gap in its magnetic circuit so that its pick-up and drop-out current values are as c ose together-as possible. The arrangement of Fig. 2 is especially suitable for applications wherein jam conditions frequently occur before the motor gets up to speed or before all of the acceleration contactors are closed. Thus a jam condition occuring at any time causes opening of the contacts 52 and 43 and prevention of the contactors i9 and 22 from closing or droping out those contactors if they have already closed. Opening of the contactor i9 and 22 reinserts all of the acceleration resistance into the motor circuit to protect the motor. The pick-up and drop-out current values oi the switch 50 are so selected that pumping does not occur. A resistor 55 relatively low ohmic value may be permanently connected in series with the motor if desired to prevent excessive current surges in event the motor comes to a sudden stop before the last acceleration contactor 22 closes. If a jam condition occurs after the contactor 22 has closed, the jam contactor 25 responds to insert the jam resistor 24 into the circuit before the current can rise to a dangerous value and before operation of the switch 50 can cause drop-out of the contactors l9 and 22. In certain applications, as for example the side guard drive of a rolling mill, it may be desired to have the pick-up value of the contactor 25 equal to or above that of the switch 50 so that the guard may be kept moving when it strikes an ingot that can be moved, the sudden but temporary rise in current due to the sudden application of such a high inertia load not causing operation of either the contactor 25 or the switch 50.

While I have described a particular embodiment of my invention and certain apparatus for carrying out my method, it will be obvious to those skilled in the art that various modifications may be made without departing from the spirit of my invention, and I therefore desire to cover all such modifications as fall within the scope of my invention which is set forth in the appended claims.

What is claimed is:

1. In a motor starting system in combination a motor armature, current supply terminals, a jam resistor, a plurality of accelerating resistors connected in series with said current supply terminals and said motor armature, a plurality of accelerating contactor-s connected in loop circuits with said accelerating resistors respectively, means for closing said contactors in succession, a normally closed jam contactor connected across said jam resistor, and an actuating coil for said jam contactor connected in series with and in the loop circuit of the accelerating contactor which closes last in succession.

2. In a motor control system the combination of current supply terminals, an electric motor, a. jam resistor, and a plurality of accelerating resistors, all connected in series, normally open accelerating contactors connected in loop circuits with said accelerating resistors respectively, a normally closed jam contactor connected across said jam resistor, and an actuating coil for said normally closed jam contactor connected in series with and in the loop circuit of one of said accelerating contactors.

3. In combination with a motor having accelerating resistors and normally open accelerating contactors in loop circuits with said resistors, respectively, adapted to close successively, a jam resistor connected in series with said motor, a normally closed jam contactor connected across said jam resistor, and an actuating coil for said jam contactor connected in series with and in the loop circuit of one of said accelerating contactors.

4. In a control system for an electric motor, means for controlling the magnitude of the motor starting current including resistance having accelerating contacts in loop circuits with portions thereof, a jam current reducing resistor for connection in series with the motor, normally closed contacts connected across said jam resistor, and an actuating coil for said normally closed conta cts connected in series with and in the loop circult of one of said accelerating contacts.

5. In combination an electric motor, a jam current reducing-resistor, a plurality of accelerating resistors, and current supply terminals to which said elements are connected in series, accelerating contactors connected in loop circuit with said accelerating resistors respectively, said contactorr. being adapted to close in succession for accelerating the motor, normally closed jam contacts across the jam current reducing resistor, and an actuating coil for said Jam contacts connected in series with and in the loop circuit of one of said accelerating contactors, said jam current reducing resistor having a different resistance value from the total resistance oi said accelerating resistors.

6. In combination an electric motor, a jam current reducing resistor, a plurality of accelerating resistors, and current supply terminals to which said elements are connected in series, accelerating contactors connected in loop circuits with said accelerating resistors respectively, said contactors being adapted to close in succession for accelerating the motor, normally closed jam contacts across the jam current reducing resistor, and an actuating coil for said jam contacts connected in series with and in the loop circuit of one of said accelerating contactors, said jam current reducing resistor having a diflerent resistance value from any of said accelerating resistors.

'I. The method of operating an electric motor which comprises starting the motor by successive increments of applied voltage, controlling the time intervals between successive increments in accordance with the magnitude of accelerating current and, after the next to the last increment has taken place, reducing the current substantially instantaneously whenever the current exceeds a. predetermined value.

8. In combination, an electric motor, accelerating resistors in series therewith, contactors for cutting out said resistors, slow acting means or introducing said resistors in the event of accelerating current peaks exceeding predetermined values, a jam current resistor in series with said motor and a jam contactor of the fast acting type for introducing said Jam current resistor in the event 01. flow of current exceeding a predetermined value.

9. In combination, a motor starter comprising means operable in time-delayed sequence for controlling the starting current of a motor, a jam current reducing resistor arranged to be connected in series with the motor, fast acting jam current control means having normally closed contacts connected across said jam resistor, and means for causing substantially instantaneous opening 01' said contacts upon occurence of a Jam condition of said motor after operation of said first named means.

10. In combination, an electric motor, a plurality oi. starting resistors connected in series therewith, accelerating contactors operable in time delayed sequence connected in loop circuits with said resistors respectively, a jam current reducing resistor connected in series with said motor, fast acting jam-current control means having normally closed contacts connected across said jam resistor and an actuating coil for causing substantially instantaneous opening of said jam contacts, said coil being connected in series with and in the loop circuit of one of said accelerating contactors.

11. The method of operating an electric motor which comprises starting the motor by successive increments of applied voltage, and, after a predetermined number ot increments of applied voltage have taken place, reducing the current subserting said jam current resistor after the said 10 cont-actor means have operated, and second jam current control means for reducing motor current independently of the operation of said accelerating contactor means.

13. In combination, an electric motor, a plurality of starting resistors connected in series therewith, accelerating contactors connected across said resistors, a jam current reducing resistor connected in series with said motor, normally closed jam contacts connected across said jam resistor having an actuating coil connected in series with one of said accelerating contactors for causing insertion of said jam resistor in series with the motor in response to current exceeding a predetermined value after the said last mentioned accelerating contactor has closed, and a second jam contactor having an actuating winding in series with said motor for insuring open condition of said accelerating contactors in response to motor current exceeding a predetermined value either beiore or after closing of the accelerating contactors.

14. In combination, an electric motor, a plurality of starting resistors connected in series therewith, accelerating contactors connected across said resistors, a jam current reducing resistor connected in series with said motor, a normally closed jam contactor connected across said jam resistor having an actuating coil connected in series with one or said accelerating contactors for causing insertion of said i am resistor in series with the motor in response to current exceeding a predetermined value after the said last mentioned accelerating contactor has closed, and a second jam contactor having an actuating windin: in series with said motor for causing open condition of said accelerating contactors in response to motor current exceeding a predetermined value either before or after closing of the accelerating contactor, said first jam contactor having a higher pick-up value than the second jam contactor.

15. In combination, an electric motor, a plurality of starting resistors connected in series therewith, accelerating contactors connected across said resistors, a jam current reducing resistor connected in series with said motor, normally closed jam contacts connected across said jam resistor having an actuating coil connected in series with one of said accelerating contactors for causing insertion of said jam resistor in series with the motor in response to current exceeding a predetermined value after the said last mentioned accelerating contactor has closed, and a second jam contactor having an actuating winding in series with said motor for causing open condition of said accelerating contactors in response to motor current exceeding a predeter-- mined value eithefbefore or after closing of the accelerating contactors, said second jam contactor having a magnetic circuit with a relatively large air gap therein so as to cause the pick-up and drop-out current values of the contactor to be relatively close together.

16. The method of operating an electric motor which comprises starting the motor by succes-- sive increments of applied voltage, controlling the time intervals between successive increments in accordance with the magnitude of accelerating current, reducing the current whenever the accelerating current exceeds a predetermined value, and after the next to the last increment has taken place, reducing the current substantially instantaneously whenever the current exceeds a predetermined value.

ZEBULON W. WHITEHOUSE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 911,013 James Jan. 26, 1909 969,583 White Sept. 6, 1910 1,513,958 Bergmann Nov. 4, 1924 

